Thanks for the likes guys and g'day to Kimba in Australia.
Only the clip shown on the youtube image is done with Natron. It takes some getting used to but I think we will hear a lot more about it.
I was very impressed with the Kdenlive appimage I used. Apparently a new version is out in late November.
I used 'Composite and Transform' from Kdenlive. It lets you fade in or out from 0% opacity.
Where the top clip overlaps the lower clip you can keyframe the alpha between 0% and 100%. I used 4 keyframes so the clip starts playing before the last one has finished. I did the opposite at the other end. The effect is you don't really notice when a clips starts or finishes.